view tests/test-narrow-widen.t @ 40326:fed697fa1734

sqlitestore: file storage backend using SQLite

This commit provides an extension which uses SQLite to store file
data (as opposed to revlogs).

As the inline documentation describes, there are still several
aspects to the extension that are incomplete. But it's a start.
The extension does support basic clone, checkout, and commit
workflows, which makes it suitable for simple use cases.

One notable missing feature is support for "bundlerepos." This is
probably responsible for the most test failures when the extension
is activated as part of the test suite.

All revision data is stored in SQLite. Data is stored as zstd
compressed chunks (default if zstd is available), zlib compressed
chunks (default if zstd is not available), or raw chunks (if
configured or if a compressed delta is not smaller than the raw
delta). This makes things very similar to revlogs.

Unlike revlogs, the extension doesn't yet enforce a limit on delta
chain length. This is an obvious limitation and should be addressed.
This is somewhat mitigated by the use of zstd, which is much faster
than zlib to decompress.

There is a dedicated table for storing deltas. Deltas are stored
by the SHA-1 hash of their uncompressed content. The "fileindex" table
has columns that reference the delta for each revision and the base
delta that delta should be applied against. A recursive SQL query
is used to resolve the delta chain along with the delta data.

By storing deltas by hash, we are able to de-duplicate delta storage!
With revlogs, the same deltas in different revlogs would result in
duplicate storage of that delta. In this scheme, inserting the
duplicate delta is a no-op and delta chains simply reference the
existing delta.

When initially implementing this extension, I did not have
content-indexed deltas and deltas could be duplicated across files
(just like revlogs). When I implemented content-indexed deltas, the
size of the SQLite database for a full clone of mozilla-unified
dropped:

before: 2,554,261,504 bytes
after:  2,488,754,176 bytes

Surprisingly, this is still larger than the bytes size of revlog
files:

revlog files: 2,104,861,230 bytes
du -b:        2,254,381,614

I would have expected storage to be smaller since we're not limiting
delta chain length and since we're using zstd instead of zlib. I
suspect the SQLite indexes and per-column overhead account for the
bulk of the differences. (Keep in mind that revlog uses a 64-byte
packed struct for revision index data and deltas are stored without
padding. Aside from the 12 unused bytes in the 32 byte node field,
revlogs are pretty efficient.) Another source of overhead is file
name storage. With revlogs, file names are stored in the filesystem.
But with SQLite, we need to store file names in the database. This is
roughly equivalent to the size of the fncache file, which for the
mozilla-unified repository is ~34MB.

Since the SQLite database isn't append-only and since delta chains
can reference any delta, this opens some interesting possibilities.
For example, we could store deltas in reverse, such that fulltexts
are stored for newer revisions and deltas are applied to reconstruct
older revisions. This is likely a more optimal storage strategy for
version control, as new data tends to be more frequently accessed
than old data. We would obviously need wire protocol support for
transferring revision data from newest to oldest. And we would
probably need some kind of mechanism for "re-encoding" stores. But
it should be doable.

This extension is very much experimental quality. There are a handful
of features that don't work. It probably isn't suitable for day-to-day
use. But it could be used in limited cases (e.g. read-only checkouts
like in CI). And it is also a good proving ground for alternate
storage backends. As we continue to define interfaces for all things
storage, it will be useful to have a viable alternate storage backend
to see how things shake out in practice.

test-storage.py passes on Python 2 and introduces no new test failures on
Python 3. Having the storage-level unit tests has proved to be insanely
useful when developing this extension. Those tests caught numerous bugs
during development and I'm convinced this style of testing is the way
forward for ensuring alternate storage backends work as intended. Of
course, test coverage isn't close to what it needs to be. But it is
a start. And what coverage we have gives me confidence that basic store
functionality is implemented properly.

Differential Revision: https://phab.mercurial-scm.org/D4928

#testcases flat tree
  $ . "$TESTDIR/narrow-library.sh"

#if tree
  $ cat << EOF >> $HGRCPATH
  > [experimental]
  > treemanifest = 1
  > EOF
#endif

  $ hg init master
  $ cd master
  $ cat >> .hg/hgrc <<EOF
  > [narrow]
  > serveellipses=True
  > EOF

  $ mkdir inside
  $ echo 'inside' > inside/f
  $ hg add inside/f
  $ hg commit -m 'add inside'

  $ mkdir widest
  $ echo 'widest' > widest/f
  $ hg add widest/f
  $ hg commit -m 'add widest'

  $ mkdir outside
  $ echo 'outside' > outside/f
  $ hg add outside/f
  $ hg commit -m 'add outside'

  $ cd ..

narrow clone the inside file

  $ hg clone --narrow ssh://user@dummy/master narrow --include inside
  requesting all changes
  adding changesets
  adding manifests
  adding file changes
  added 2 changesets with 1 changes to 1 files
  new changesets *:* (glob)
  updating to branch default
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ cd narrow
  $ hg tracked
  I path:inside
  $ ls
  inside
  $ cat inside/f
  inside
  $ cd ..

add more upstream files which we will include in a wider narrow spec

  $ cd master

  $ mkdir wider
  $ echo 'wider' > wider/f
  $ hg add wider/f
  $ echo 'widest v2' > widest/f
  $ hg commit -m 'add wider, update widest'

  $ echo 'widest v3' > widest/f
  $ hg commit -m 'update widest v3'

  $ echo 'inside v2' > inside/f
  $ hg commit -m 'update inside'

  $ mkdir outside2
  $ echo 'outside2' > outside2/f
  $ hg add outside2/f
  $ hg commit -m 'add outside2'

  $ echo 'widest v4' > widest/f
  $ hg commit -m 'update widest v4'

  $ hg log -T "{if(ellipsis, '...')}{rev}: {desc}\n"
  7: update widest v4
  6: add outside2
  5: update inside
  4: update widest v3
  3: add wider, update widest
  2: add outside
  1: add widest
  0: add inside

  $ cd ..

Widen the narrow spec to see the widest file. This should not get the newly
added upstream revisions.

  $ cd narrow
  $ hg tracked --addinclude widest/f
  comparing with ssh://user@dummy/master
  searching for changes
  no changes found
  saved backup bundle to $TESTTMP/narrow/.hg/strip-backup/*-widen.hg (glob)
  adding changesets
  adding manifests
  adding file changes
  added 3 changesets with 2 changes to 2 files
  new changesets *:* (glob)
  $ hg tracked
  I path:inside
  I path:widest/f

  $ cat widest/f
  widest

Pull down the newly added upstream revision.

  $ hg pull
  pulling from ssh://user@dummy/master
  searching for changes
  adding changesets
  adding manifests
  adding file changes
  added 5 changesets with 4 changes to 2 files
  new changesets *:* (glob)
  (run 'hg update' to get a working copy)
  $ hg update -r 'desc("add wider")'
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ cat widest/f
  widest v2

  $ hg update -r 'desc("update inside")'
  2 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ cat widest/f
  widest v3
  $ cat inside/f
  inside v2

  $ hg log -T "{if(ellipsis, '...')}{rev}: {desc}\n"
  7: update widest v4
  ...6: add outside2
  5: update inside
  4: update widest v3
  3: add wider, update widest
  ...2: add outside
  1: add widest
  0: add inside

Check that widening with a newline fails

  $ hg tracked --addinclude 'widest
  > '
  abort: newlines are not allowed in narrowspec paths
  [255]

widen the narrow spec to include the wider file

  $ hg tracked --addinclude wider
  comparing with ssh://user@dummy/master
  searching for changes
  no changes found
  saved backup bundle to $TESTTMP/narrow/.hg/strip-backup/*-widen.hg (glob)
  adding changesets
  adding manifests
  adding file changes
  added 8 changesets with 7 changes to 3 files
  new changesets *:* (glob)
  $ hg tracked
  I path:inside
  I path:wider
  I path:widest/f
  $ hg update 'desc("add widest")'
  2 files updated, 0 files merged, 1 files removed, 0 files unresolved
  $ cat widest/f
  widest
  $ hg update 'desc("add wider, update widest")'
  2 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ cat wider/f
  wider
  $ cat widest/f
  widest v2
  $ hg update 'desc("update widest v3")'
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ cat widest/f
  widest v3
  $ hg update 'desc("update widest v4")'
  2 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ cat widest/f
  widest v4

  $ hg log -T "{if(ellipsis, '...')}{rev}: {desc}\n"
  7: update widest v4
  ...6: add outside2
  5: update inside
  4: update widest v3
  3: add wider, update widest
  ...2: add outside
  1: add widest
  0: add inside

separate suite of tests: files from 0-10 modified in changes 0-10. This allows
more obvious precise tests tickling particular corner cases.

  $ cd ..
  $ hg init upstream
  $ cd upstream
  $ cat >> .hg/hgrc <<EOF
  > [narrow]
  > serveellipses=True
  > EOF
  $ for x in `$TESTDIR/seq.py 0 10`
  > do
  >   mkdir d$x
  >   echo $x > d$x/f
  >   hg add d$x/f
  >   hg commit -m "add d$x/f"
  > done
  $ hg log -T "{rev}: {desc}\n"
  10: add d10/f
  9: add d9/f
  8: add d8/f
  7: add d7/f
  6: add d6/f
  5: add d5/f
  4: add d4/f
  3: add d3/f
  2: add d2/f
  1: add d1/f
  0: add d0/f

make narrow clone with every third node.

  $ cd ..
  $ hg clone --narrow ssh://user@dummy/upstream narrow2 --include d0 --include d3 --include d6 --include d9
  requesting all changes
  adding changesets
  adding manifests
  adding file changes
  added 8 changesets with 4 changes to 4 files
  new changesets *:* (glob)
  updating to branch default
  4 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ cd narrow2
  $ hg tracked
  I path:d0
  I path:d3
  I path:d6
  I path:d9
  $ hg verify
  checking changesets
  checking manifests
  checking directory manifests (tree !)
  crosschecking files in changesets and manifests
  checking files
  checked 8 changesets with 4 changes to 4 files
  $ hg log -T "{if(ellipsis, '...')}{rev}: {desc}\n"
  ...7: add d10/f
  6: add d9/f
  ...5: add d8/f
  4: add d6/f
  ...3: add d5/f
  2: add d3/f
  ...1: add d2/f
  0: add d0/f
  $ hg tracked --addinclude d1
  comparing with ssh://user@dummy/upstream
  searching for changes
  no changes found
  saved backup bundle to $TESTTMP/narrow2/.hg/strip-backup/*-widen.hg (glob)
  adding changesets
  adding manifests
  adding file changes
  added 9 changesets with 5 changes to 5 files
  new changesets *:* (glob)
  $ hg tracked
  I path:d0
  I path:d1
  I path:d3
  I path:d6
  I path:d9
  $ hg log -T "{if(ellipsis, '...')}{rev}: {desc}\n"
  ...8: add d10/f
  7: add d9/f
  ...6: add d8/f
  5: add d6/f
  ...4: add d5/f
  3: add d3/f
  ...2: add d2/f
  1: add d1/f
  0: add d0/f

Verify shouldn't claim the repo is corrupt after a widen.

  $ hg verify
  checking changesets
  checking manifests
  checking directory manifests (tree !)
  crosschecking files in changesets and manifests
  checking files
  checked 9 changesets with 5 changes to 5 files

Widening preserves parent of local commit

  $ cd ..
  $ hg clone -q --narrow ssh://user@dummy/upstream narrow3 --include d2 -r 2
  $ cd narrow3
  $ hg log -T "{if(ellipsis, '...')}{rev}: {desc}\n"
  1: add d2/f
  ...0: add d1/f
  $ hg pull -q -r 3
  $ hg co -q tip
  $ hg pull -q -r 4
  $ echo local > d2/f
  $ hg ci -m local
  created new head
  $ hg tracked -q --addinclude d0 --addinclude d9

Widening preserves bookmarks

  $ cd ..
  $ hg clone -q --narrow ssh://user@dummy/upstream narrow-bookmarks --include d4
  $ cd narrow-bookmarks
  $ echo local > d4/f
  $ hg ci -m local
  $ hg bookmarks bookmark
  $ hg bookmarks
   * bookmark                  3:* (glob)
  $ hg -q tracked --addinclude d2
  $ hg bookmarks
   * bookmark                  5:* (glob)
  $ hg log -r bookmark -T '{desc}\n'
  local

Widening that fails can be recovered from

  $ cd ..
  $ hg clone -q --narrow ssh://user@dummy/upstream interrupted --include d0
  $ cd interrupted
  $ echo local > d0/f
  $ hg ci -m local
  $ hg log -T "{if(ellipsis, '...')}{rev}: {desc}\n"
  2: local
  ...1: add d10/f
  0: add d0/f
  $ hg bookmarks bookmark
  $ hg --config hooks.pretxnchangegroup.bad=false tracked --addinclude d1
  comparing with ssh://user@dummy/upstream
  searching for changes
  no changes found
  saved backup bundle to $TESTTMP/interrupted/.hg/strip-backup/*-widen.hg (glob)
  adding changesets
  adding manifests
  adding file changes
  added 3 changesets with 2 changes to 2 files
  transaction abort!
  rollback completed
  abort: pretxnchangegroup.bad hook exited with status 1
  [255]
  $ hg log -T "{if(ellipsis, '...')}{rev}: {desc}\n"
  $ hg bookmarks
  no bookmarks set
  $ hg unbundle .hg/strip-backup/*-widen.hg
  adding changesets
  adding manifests
  adding file changes
  added 3 changesets with 2 changes to 1 files
  new changesets *:* (glob)
  (run 'hg update' to get a working copy)
  $ hg log -T "{if(ellipsis, '...')}{rev}: {desc}\n"
  2: local
  ...1: add d10/f
  0: add d0/f
  $ hg bookmarks
   * bookmark                  2:* (glob)